It is essential in a gas turbine engine to monitor the speed of the rotating parts. In the past, this has been accomplished through the use of magnetic or optical sensors that can detect shaft or rotor speed. Sensors of this type are sensitive to heat and contamination and therefore are restricted in use to the cooler, less dirty, portions of the engine, i.e. compressor, bearings, and forward shafting. The information provided by these systems is, therefore, limited and will not necessarily indicate rotor conditions in the turbine section. This becomes critical if there is a compressor turbine shaft failure forward of the speed sensor. The indicator of the prior art would show a slowing down of the compressor and call for an increase in fuel to compensate for the declining speed, when in actuality the compressor turbine, free of its load, is beginning to accelerate to rotational speeds which may cause it to break apart.
It is the purpose of this invention to provide a probe which can withstand the turbine nozzle environment, the temperatures of which may exceed 1600.degree. F. and which is dense in the products of combustion. This probe can generate a signal which can be used for tip clearance control, speed monitoring, and other purposes depending on the electronic analysis of the signal. This particular application will describe a speed monitoring system.